A number of recent studies have noted associations between violence, substance use, and risk of infection with HIV. However, the prevalence patterns, and predictors of their co-occurrence are unknown. Nor are the reasons for their association well understood. The proposed studies use data from a panel of over 3600 young adults of diverse social and economic backgrounds to explore these issues, employing both cross- sectional and longitudinal approaches. Study 1 will estimate the prevalence of high-risk sexual activity, injection drug use, and various types of violence, victimization, and substance use among heterosexual adults aged 23-24. Rates for various patterns of co-occurrence among these problems will also be estimated and the characteristics of persons with multiple problems will be determined. Studies 2 and 3 will explore the basis for co-occurring problems in adulthood: the first will focus on concurrent relationships and predictors; the second will examine prospective predictors. These studies will identify the common and unique predictors of violence, victimization, substance use, HIV sexual risk and risk for HIV from injection drug use to test whether multiple problems might be co-morbid outcomes of a risk-enhancing personality or environment. They all explore possible direct relationships between HIV risk and other high-risk problems. They examine whether problems with violence and use of drugs make a unique contribution to HIV risk, over and above the influence of other personal and environmental factor, and whether substance use and violence mediate the impact of other factors on HIV risk. Importantly, each of these predictors and their relationships to HIV risk are tested at early adolescence, late adolescence, and young adulthood, allowing us to determine whether early substance use or early experience with violence and sexual activity makes a contribution to adult HIV risk independent of other adult and adolescent predictive factors.